You have probably not heard of this gem before. Gem silica is a rare variety of greenish blue chalcedony. Small amounts are currently produced in Arizona and a few other locations. It is the rarest and the most expensive variety of chalcedony.

Gem silica receives its wonderful color from small amounts of included chrysocolla or copper compounds. It is found in arid areas, in the rocks above copper deposits.

Gem silica has a Mohs hardness of 7 and is a very tough stone. That makes it perfect for use in almost any kind of jewelry.

You will probably never see gem silica in a mall jewelry store or in a department store. Gem silica is primarily used by high-end jewelry designers who are making one-of-a-kind jewelry items. At the present time (late 2015) it does not have an astronomical price. The 1.5-carat trillion-cut stone in the photo had a retail price of $179.